Brewster's Warbler

I recently photographed a Brewster's Warbler in Orange County, NY. It may be a backcross between a Brewster's and a Golden-winged as it has a white breast only slightly tinged with yellow. Then again, it may just be a first-year Brewster's. It's hard to tell with these hybrids. Photos begin here.

According to the Cornell Ornithology Lab:

Scientists have identified dozens of hybrid crosses between warbler species. Although most combinations are very rare, a few crosses are common enough to be encountered with some regularity. The best known are the hybrids between Blue-winged and Golden-winged warblers, which are depicted in many field guides. Hybrids between these species typically show stereotyped plumage patterns that combine traits from both of the parental species. The most common hybrid form is known as a "Brewster's" warbler; the rarer form is known as a "Lawrence's" warbler. We currently believe that a "Lawrence's" warbler results when two "Brewster's" warblers mate, or when a "Brewster's" warbler backcrosses with one of its parent species, but research into the genetics of hybridization between these species is underway and many questions remain unanswered.